The present invention relates to an error protection method and an error protection device that protects a variety of data from signal errors in the process of transmission.
Error protection has been performed on data such as voice and images to protect it from signal errors while being transmitted. A variety of error protection methods have been employed, such as PDC half-rate, Twin-VQ, and the like.
In addition, the error protection methods of the prior art were applied to fixed length frames with the same number of bits per frame, or to quasi-fixed length frames where frames of a limited variety of bit lengths only were to be found.
In the prior art error protection method, the error sensitivity was examined for each parameter (including bits) making up the frame, and in the case of parameters with high sensitivity, error protection of a specified type (e.g., the addition of an error detection code or error correction encoding) was performed on frames containing parameters with high sensitivity at the time of transmitting the frames. Here, the error sensitivity of the parameter is of a degree that would degrade the results of decoding obtained on the receiving side, in the case where a single error bit occurred in the process of transmitting said parameter.
FIG. 13 shows an example of the configuration of a prior art error protection device. In this figure, a class sorter 401 takes the frame that is to be error protected, and sorts the parameters of the frame into classes according to their respective degrees of error sensitivity.
In the case of this error protection device, the error protection method, namely either error correction encoding at a specified encoding ratio, or the addition of a specified error detection code, is determined for each class.
A class data error protection processing part 403 implements the error correction encoding or adds an error detection code, according to the error protection method determined in response to the various classes, with respect to the various parameters classified into said classes. Specifically, convolution is carried out for error correction encoding, and cyclic redundancy encoding is carried out to produce an error detection code. Furthermore, an output device 404 performs interleaving and the like on the data that undergoes error correction encoding or to which is added an error detection code, and sends the data to the recipient.
Incidentally, in the case of the prior art error correction device, previously established error protection was carried out for each class. Thus, the prior art error-correcting device had the drawbacks of low flexibility in methods of protection and poor general applicability.
Moreover, the prior art error protection device also had the drawback that it was unable to protect a variable length frame, the number of constituent bits thereof fluctuating with time, since it could protect only the fixed length frames or quasi-fixed length frames as mentioned above.
The present invention was devised in light of the above-described state of affairs, and has as its object to provide an error protection method and an error protection device that makes it possible to employ a variety of error-correcting algorithms, even when the frames are of a flexible length.
In order to achieve said object, the error protection method relating to the present invention includes a process for sorting a plurality of parameters making up a frame into a plurality of classes, a process for generating frame-forming data containing data relating to the formation of said frame and data with an error protection method determined for each class to be applied to the said parameters, a process for implementing the specified error protection to said frame-forming data, a process for implementing error protection specified for each class according to the said frame-forming data, with respect to the data sorted into the said plurality of classes, and a process for transmitting the frame-forming data that has undergone said specified error protection and parameters that were error protected for each said class.
In accordance with the invention, since the parameters are divided into classes, and since the devices are arranged separately so there is a device for generating frame-forming data indicating the content of the error protection to be performed for each class, and a device for performing protection corresponding to each class according to the frame-forming data, it is possible to adjust to changes in the content of the error protection to be applied to each class.
Furthermore, since frame-forming data is transmitted that indicates what type of error protection is suited for each class, the content of the error protection that is to be applied to each class is taken from this frame-forming data by the receiving side device, making it possible to respond appropriately. Therefore, there is no need to fix the content of the error protection, and it becomes possible to switch the error protection content between the transmission side device and the receiving side device, as expediency may dictate. In addition, since the frame-forming data contains data pertaining to the formation of frames, it is possible to implement the processing of variable length frames that have undergone error protection by the receiving side device.